Mobility overestimation due to gated contacts in organic field-effect transistors

• Published in: Nature communications 2016-03, Vol.7 (1), p.10908-10908, Article 10908
• Main Authors: Bittle, Emily G., Basham, James I., Jackson, Thomas N., Jurchescu, Oana D., Gundlach, David J.
• Format: Article
• Language: English
• Subjects: 639/301/119/995; 639/766/25; Dielectric Spectroscopy; Humanities and Social Sciences; Materials Testing; multidisciplinary; Naphthacenes - chemistry; Science; Science (multidisciplinary); Silicon Dioxide - chemistry; Transistors, Electronic
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms10908

Parameters used to describe the electrical properties of organic field-effect transistors, such as mobility and threshold voltage, are commonly extracted from measured current–voltage characteristics and interpreted by using the classical metal oxide–semiconductor field-effect transistor model. However, in recent reports of devices with ultra-high mobility (>40 cm 2  V −1  s −1 ), the device characteristics deviate from this idealized model and show an abrupt turn-on in the drain current when measured as a function of gate voltage. In order to investigate this phenomenon, here we report on single crystal rubrene transistors intentionally fabricated to exhibit an abrupt turn-on. We disentangle the channel properties from the contact resistance by using impedance spectroscopy and show that the current in such devices is governed by a gate bias dependence of the contact resistance. As a result, extracted mobility values from d.c. current–voltage characterization are overestimated by one order of magnitude or more. Charge mobility, extracted from current–voltage curves, is an important parameter for evaluating the performance of organic field-effect transistors. Bittle et al . show that charge mobility can be overestimated by one order of magnitude due to the gate bias dependence of the charge injection process.